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When we consider the perception of the horizon on a flat Earth, we must imagine a completely unobstructed line of sight that extends indefinitely. On a flat plane, the horizon would appear as a straight line. Ships, mountains, or any distant objects would come into view without being obstructed by the Earth's surface.

In contrast, on our actual spherical Earth, the horizon is curved due to Earth's curvature. We perceive this curvature most obviously when viewing expansive areas of water like oceans. However, on a flat Earth, the horizon would seem endlessly flat and objects would not disappear from view as they do in reality. This straightforward perspective greatly contrasts with our actual observation experiences.

The way we see ships approaching us can reveal a lot about the shape of Earth. If Earth were flat, a ship at a distance would continuously get bigger as it approached. All parts of it, from the hull to the mast, would be seen simultaneously and completely as it moved closer.

On the spherical Earth, this isn't the case. As a ship moves towards us, the lower part, the hull, starts to vanish first, due to the Earth's curvature. Only the upper parts, such as the mast, remain visible for a longer period. This effect, often observed at sea, gives a key piece of evidence favoring the globe model over a flat one.

Earth's curvature is a central concept when discussing the shape of our planet. It implies that Earth's surface bends and creates a continuous curve that eventually brings every point back to itself in three-dimensional space.

This curvature impacts how we see distant objects. As the Earth curves, the ground between an observer and distant objects creates an obstructing effect. Objects move below the horizon as they get further away, with their lower parts disappearing first. This natural phenomenon means that our perception of objects changes with distance, illustrating the three-dimensional curve Earth possesses.

Visual observation is our primary means of understanding Earth’s shape. From our standpoint on Earth's surface, our eyes gather information about the environment, including noticeable phenomena like how objects disappear from bottom to top when they move beyond the horizon.

These observations are integral to determining the nature of Earth's form. For example, by observing at a distance, the gradual vanishing of the lower parts of ships until only the upper parts are seen strongly suggests curvature. This is a tangible experience implicating the Earth isn't flat, underpinning the argument that visual perception aligns with a spherical Earth.